1. Field of the Invention
The present invention relates to a lens-fitted photo film unit to make exposure through an exposure aperture. More particularly, the present invention relates to a lens-fitted photo film unit to ensure flash light emission at the time when the exposure aperture is fully open.
2. Description Related to the Prior Art
A lens-fitted photo film unit has a simple photography mechanism, such as a struck-type shutter mechanism that has a shutter blade to open and close an exposure aperture. Since a photo filmstrip is preloaded in the lens-fitted photo film unit in manufacture, a user can enjoy photography right after the purchase of the lens-fitted photo film unit.
Some lens-fitted photo film units have flash devices to emit flash light to increase exposure amount in indoor or night photography. The flash device has a flash circuit that includes a main capacitor, a flash discharge tube and a synchronization switch. The synchronization switch has a pair of metal plates. In photography, the shutter blade is rotated to press one metal plate onto the other metal plate so that the synchronization switch is turned on. When the main capacitor is charged at that time, the synchronization switch outputs a trigger signal to discharge the electrons in the main capacitor to the flash discharge tube, so that flash light is emitted to increase exposure amount of a main subject.
With the flash device of the lens-fitted photo film unit, however, it is difficult to apply enough amount of flash light to a background behind the main subject. When indoor or night photography is carried out with flash device, the background on the exposed image is much darker than the main subject.
In order to deal with this problem, Japanese laid-open patent (JP-A) 11-326987 discloses a lens-fitted photo film unit that enables multiple shutter speeds by moving a stopper to limit the rotation of the shutter blade. Exposure amount of the background is increased in indoor or night photography by making the shutter speed slower.
In order to prevent failure exposure due to camera-shake, it is desirable to shorten the exposure time by making the shutter speed faster. Thus, various improvements, such as a photo filmstrip with higher sensitivity and a brighter taking lens, are applied to the lens-fitted photo film unit. It is necessary to start flash light emission at the time when the exposure aperture is fully open. Shorter exposure time makes it difficult to start flash light emission at the appropriate timing during exposure.
Moreover, the metal plates of the synchronization switch are bent upon being pressed by the shutter blade. If bending characteristics of the metal plates is changed, or if the metal plates are deformed after plural photography, time lag between flash light emission and exposure is happened. Such time lag causes under exposure.
It is also possible to control the shutter speed by providing kinds of lens-fitted photo film units with different shutter speeds. These lens-fitted photo film units have stoppers to limit the rotation of the shutter blade. The stoppers are fixed at different positions. Such lens-fitted photo film units do not include a mechanism to move the stopper, so it is possible to reduce the manufacture cost of the lens-fitted photo film unit.
Although these lens-fitted photo film units have different mechanical parts, it is preferable to use common parts as many as possible in order to increase the productivity and reduce the manufacture cost.
An object of the present invention is to provide a lens-fitted photo film unit that ensures flash light emission at an appropriate timing in photography at a fast shutter speed.
Another object of the present invention is to increase the productivity of the lens-fitted photo film units with different shutter speeds.
To achieve the above objects, the lens-fitted photo film unit has a stopper to limit the movement of a shutter lever, and the stopper is provided at a position in contact to or near one of two contact plates of a synchronization switch of a flash device. When a shutter blade presses the first contact plate onto the second contact plate at a position to open the exposure aperture, the stopper holds the shutter blade, the first and second contact plates to limit the movement of said shutter blade.
The lens-fitted photo film unit is manufactured by attaching the stopper at a position in contact to or near the second contact plate. A lens-fitted photo film unit without the stopper has a slower shutter speed, compared to the one with the stopper, because the rotation of the shutter blade is not limited. It is possible to provide plural lens-fitted photo film unit with different shutter speeds by attaching or removing the stopper.
In the preferred embodiment, the stopper is attached to a lens cover in the rotatable manner, and is movable between a fast shutter speed position in contact to or near the second contact plate and a slow shutter speed position away from the second contact plate. At the fast shutter speed position, the stop lever holds the shutter blade, the first and second contact plates to limit the rotation of the shutter blade at the open position.
One end portion of the stop lever at the fast shutter speed position is moved to the free end side of the second contact plate. The end portion of the stop lever prevents the second contact plate from being deformed when the first contact plate presses the second contact plate in exposure.
The lens-fitted photo film unit may have an operation member, a movable aperture plate and changeover means to move the stop lever according to the operation of the operation member. The operation member is preferably movable between a first position to turn off the flash device, a second position to turn on the flash device and holds the stop lever at the fast shutter speed position, and a third position to turn on the flash device and holds the stop lever at the slow shutter speed position. The changeover means preferably set a small aperture state when the stop lever is at the fast shutter speed position, and preferably set a large aperture state when the stop lever is at the slow shutter speed position.
According to the present invention, the stopper or the stop lever supports one of the contact plates of the synchronization switch of the flash device, so it is possible to ensure flash light emission at an appropriate timing even though the shutter speed becomes faster. Moreover, it is possible to increase productivity of the lens-fitted photo film units with different shutter speeds by using common mechanical and electrical components other than the stopper or the stop lever.